People use the word gender to indicate your biological sex or your sense of being female, male, or a combination of both. Danica Patrick is someone who has broken many gender barriers by being a successful female race-car driver in a male-dominated sport.
If you've learned French, Spanish, or Latin, you know these languages assign genders to nouns, such as masculine, feminine, or neuter. Besides this grammatical use, gender and sex are very often used as synonyms in everyday speech. However, while sex refers to biological differences between men and women, gender is much more complicated and changeable, influenced by society, culture, and an individual person's self-identity.